The human eye has two principal anatomical segments: the anterior segment and the posterior segment. The anterior segment includes the cornea, iris, lens, ciliary body, and the anterior portion of the sclera. It also includes the anterior chamber, which lies between the cornea and the iris, and the posterior chamber, which lies between the iris and the lens. Both the anterior and posterior chambers are filled with aqueous humor.
Many disorders, such as cataracts, ulcers, pterygia, and angle-closure glaucomas affect the anterior segment of the eye and can lead to blindness if left undiagnosed.
The conventional “gold standard” for screening the anterior segment of the eye is the ophthalmic slit lamp. A slit lamp comprises a high-intensity light source that may be focused to shine a thin sheet of light into the eye. Different layers of the anterior segment have different refractive indices, resulting in the scattering of light at the boundary of these layers. This sheet of light illuminates a thin slice of the eye that, when viewed at a sufficiently large angle off the optical axis of illumination, allows for viewing of a cross-sectional view of the anterior segment. Manipulation of the angle at which this sheet of light hits the surface of the eye allows for viewing different cross-sections of the eye. Various pathologies and conditions affecting the anterior segment manifest themselves as a change in refractive index and scattering properties.
The need for mechanically rotating arms to manipulate the light sheet and eyepiece constrains the form factor and size of the conventional slit lamp. A shorter arm length would result in a lower tolerance for error in position of the end of the arm, making it harder to illuminate the desired cross-section of the eye. Additionally, the presence of moving parts requires the device to be sufficiently far from the subject's eye to prevent injury.